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| United States Patent |
5,603,673
|
|
Minowa
, et al.
|
February 18, 1997
|
Change gear control device using acceleration and gear ratio as
parameters for automatic transmission in a motor vehicle and the method
therefor
Abstract
A change gear control device is provided for an automatic transmission in a
motor vehicle propelled by an internal combustion engine which is operated
with an air/fuel mixture having air/fuel ratios ranging from a fuel rich
air/fuel ratio to a fuel lean air/fuel ratio depending on driving
conditions of the motor vehicle. In this device a first detector detects
an engine torque of the internal combustion engine and a second detector
detects a vehicle speed of the motor vehicle. A processor processes
transmission gear ratios for the automatic transmission. In particular,
the processor reads the detected engine torque from the first detector and
the detected vehicle speed from the second detector, determines a new
transmission gear ratio based upon the engine torque and the vehicle
speed, and outputs a signal representing the new transmission gear ratio
to the automatic transmission, whereby a gear shifting operation is
effected at a timing based on an engine torque variation due to an
operating air/fuel ratio change.
| Inventors:
|
Minowa; Toshimichi (Toukai-mura, JP);
Kimura; Hiroshi (Hitachi, JP);
Yoshida; Yoshiyuki (Yokohama, JP);
Ohyama; Yoshishige (Katsuta, JP);
Nishimura; Yutaka (Katsuta, JP)
|
| Assignee:
|
Hitachi, Ltd. (Tokyo, JP)
|
| Appl. No.:
|
554804 |
| Filed:
|
November 7, 1995 |
Foreign Application Priority Data
| Current U.S. Class: |
477/110; 477/115; 477/120; 477/904 |
| Intern'l Class: |
F02D 043/00; B60K 041/04 |
| Field of Search: |
477/115,120,121,904,107,109
|
References Cited
U.S. Patent Documents
| 4102222 | Jul., 1978 | Miller et al. | 477/120.
|
| 4625590 | Dec., 1986 | Muller | 477/120.
|
| 4679145 | Jul., 1987 | Breck et al. | 364/424.
|
| 4739483 | Apr., 1988 | Ina et al. | 477/121.
|
| 4788892 | Dec., 1988 | Komoda et al. | 477/120.
|
| 4893526 | Jan., 1990 | Tokero | 477/43.
|
| 4930374 | Jun., 1990 | Simonyi et al. | 477/62.
|
| 4945483 | Jul., 1990 | Tokaro | 364/424.
|
| 5025684 | Jun., 1991 | Stehle et al. | 477/62.
|
| 5035160 | Jul., 1991 | Morita | 477/904.
|
| 5067374 | Nov., 1991 | Sakai et al. | 477/121.
|
| 5113721 | May., 1992 | Polly | 477/80.
|
| 5129288 | Jul., 1992 | Sasaki et al. | 477/120.
|
| 5150635 | Sep., 1992 | Minowa et al. | 477/115.
|
| 5231897 | Aug., 1993 | Morita | 477/120.
|
| 5319555 | Jun., 1994 | Iwaki et al. | 477/120.
|
| 5476425 | Dec., 1995 | Shiraishi et al. | 477/109.
|
| Foreign Patent Documents |
| 0385438 | Feb., 1990 | EP.
| |
| 3023646 | Jan., 1981 | DE.
| |
| 3621674 | Jun., 1986 | DE.
| |
| 3922040 | Jul., 1989 | DE.
| |
| 2052651 | Jan., 1981 | GB | 477/904.
|
Other References
Nikkan Jidoosher Shymbum, Oct. 15, 1992.
D. Monroe et al., "Evaluation of a Cu/Zeolite Catalyst to Remove NOx from
Lean Exhaust," SAE Technical Paper Series, pp. 195-203, Mar. 1993.
JP-1-21-255(A), Patents Abstracts of Japan, M-823 May 10, 1989 vol. 13/No.
194.
JP-1-21-256(A), Patents Abstracts of Japan, M-823 May 10, 1989 vol. 13/No.
194.
|
Primary Examiner: Ta; Khoi Q.
Attorney, Agent or Firm: Antonelli, Terry, Stout & Kraus, LLP
Parent Case Text
This application is a continuation of application Ser. No. 08/107,018 filed
Aug. 17, 1993, now U.S. Pat. No. 5,470,290, which in turn is a
continuation-in-part of application Ser. No. 07/840,816 filed Feb. 25,
1992, now U.S. Pat. No. 5,235,876 issued Aug. 17, 1993.
Claims
We claim:
1. A change transmission speed ratio control device for an automatic
transmission in a motor vehicle comprising:
a first detector for detecting an engine torque of the motor vehicle;
a second detector for detecting a vehicle speed of the motor vehicle; and
a processor for processing transmission speed ratios for the automatic
transmission, wherein said processor reads the detected engine torque from
said first detector and the detected vehicle speed from said second
detector, determines a new transmission speed ratio based upon the engine
torque and the vehicle speed, and outputs a signal representing the new
transmission speed ratio to the automatic transmission.
2. A change transmission speed ratio control device for an automatic
transmission in a motor vehicle according to claim 1, wherein said first
detector is a torque sensor.
3. A change transmission speed ratio control device for an automatic
transmission in a motor vehicle according to claims 1, wherein said motor
vehicle is propelled by an internal combustion engine which is operated
with an air/fuel mixture having air/fuel ratios ranging from a fuel rich
air/fuel ratio to a fuel lean air/fuel ratio depending on driving
conditions of the motor vehicle.
4. A change transmission speed ratio control device for an automatic
transmission in a motor vehicle according to claim 1, wherein said new
transmission speed ratio determined by said processor is selected from a
predetermined number of respective transmission speed ratios.
5. A change transmission speed ratio control device for an automatic
transmission in a motor vehicle comprising:
an acceleration sensor which detects an acceleration of the motor vehicle
in its traveling direction;
a first detector for detecting a vehicle speed of the motor vehicle;
a second detector for determining an instant transmission speed ratio of
the automatic transmission; and
a processor for processing transmission speed ratios for the automatic
transmission, wherein said processor determines the engine torque based
upon the detected acceleration from said acceleration sensor and the
instant transmission speed ratio from said second detector, and wherein
the processor further determines a new transmission speed ratio based upon
the determined engine torque and the detected vehicle speed from said
first detector, and outputs a signal representing the new transmission
speed ratio to the automatic transmission, whereby the timing of a
transmission speed ratio changing operation is effected based on an engine
torque variation due to an operating air/fuel ratio change, wherein said
motor vehicle is propelled by an internal combustion engine which is
operated with an air/fuel mixture having air/fuel ratios ranging from a
fuel rich air/fuel ratio to a lean air/fuel ratio depending on driving
conditions of the motor vehicle.
6. A change transmission speed ratio control device for an automatic
transmission in a motor vehicle according to claim 5, further comprising a
further acceleration sensor which detects an acceleration acting on the
motor vehicle in its lateral direction and an inhibitor for inhibiting the
signal representing the new transmission speed ratio from said processor
to the automatic transmission when a lateral acceleration acting on the
motor vehicle detected by said further acceleration sensor exceeds a
predetermined reference value.
7. A change transmission speed ratio control method according to claim 5,
wherein said determined new transmission speed ratio is one of a
predetermined number of respective transmission speed ratios.
8. A change transmission speed ratio control method for an automatic
transmission in a motor vehicle comprising the steps of:
detecting vehicle speed of the motor vehicle;
determining an engine torque of the internal combustion engine;
retrieving a change transmission speed ratio characteristic map having map
retrieval inputs of engine torque and vehicle speed to obtain a new
transmission speed ratio based upon the detected vehicle speed and the
determined engine torque; and
outputting a signal representing the obtained new transmission speed ratio
to the automatic transmission, whereby the timing of a transmission speed
ratio changing operation is effected based on an engine torque variation
due to an operating air/fuel ratio change, wherein said motor vehicle is
propelled by an internal combustion engine which is operated with an
air/fuel mixture having air/fuel ratios ranging from a fuel rich air/fuel
ratio to a fuel lean air/fuel ratio depending on driving conditions of the
motor vehicle.
9. A change transmission speed ratio control method according to claim 8,
wherein said obtained new transmission speed ratio is one of a
predetermined number of respective transmission speed ratios.
10. A change transmission speed ratio control method for an automatic
transmission in a motor vehicle comprising the steps of:
detecting a traveling speed of the motor vehicle;
detecting an acceleration of the motor vehicle in its traveling direction;
detecting the instant transmission speed ratio of the automatic
transmission;
calculating an engine torque based upon the detected acceleration and the
instant transmission speed ratio;
retrieving a change transmission speed ratio characteristic map having map
retrieval inputs of engine torque and vehicle travelling speed to obtain a
new transmission speed ratio based upon the detecting traveling speed and
the calculated engine torque; and
outputting a signal representing the obtained new transmission speed ratio
to the automatic transmission, whereby the timing of a transmission speed
ratio changing operation is effected based on an engine torque variation
due to an operating air/fuel ratio change, wherein said motor vehicle is
propelled by an internal combustion engine which is operated with an
air/fuel mixture having air fuel ratios ranging from a fuel rich air/fuel
ratio to a fuel lean air/fuel ratio depending on driving conditions of the
motor vehicle.
11. A change transmission speed ratio control method according to claim 10
further comprising the steps of:
detecting an acceleration acting on the motor vehicle in its lateral
direction; and
inhibiting the signal representing the obtained new transmission speed
ratio to the automatic transmission when the detected lateral acceleration
exceeds a predetermined reference value.
12. A change transmission speed ratio control method for an automatic
transmission in a motor vehicle according to claim 10, wherein said
obtained new transmission speed ratio is one of a predetermined number of
respective transmission speed ratios.
13. A change transmission speed ratio control method for an automatic
transmission in a motor vehicle comprising the steps of:
detecting an engine rotational speed of the motor vehicle;
detecting an acceleration of the motor vehicle in its traveling direction;
detecting the instant transmission speed ratio of the automatic
transmission;
calculating an engine torque based upon the detected acceleration and the
instant transmission speed ratio;
determining whether or not the calculated engine torque is a finite value;
calculating target engine rotational speeds corresponding to respective
transmission speed ratios based upon the detected engine rotational speed;
obtaining an engine rotation speed at a transmission speed ratio changing
point which is absolutely determined by the calculated engine torque;
comparing the engine rotational speed at the transmission speed ratio
changing point determined by the calculated engine torque with the
respective calculated target engine rotational speeds;
selecting the nearest calculated target engine rotational speed to the
engine rotational speed at the transmission speed ratio changing point but
below the engine rotational speed at the transmission speed ratio changing
point;
determining a new transmission speed ratio based upon the selected nearest
calculated target engine rotational speed; and
outputting a signal representing the determined new transmission speed
ratio to the automatic transmission, whereby the timing of a transmission
speed ratio changing operation is effected based on an engine torque
variation due to an operating air/fuel ratio change, wherein said motor
vehicle is propelled by an internal combustion engine which is operated
with an air/fuel mixture having air/fuel ratios ranging from a fuel rich
air/fuel ratio to a fuel lean air/fuel ratio depending on driving
conditions of the motor vehicle.
14. A change transmission speed ratio control method for an automatic
transmission in a motor vehicle according to claim 13, further comprising
the steps of:
detecting an acceleration acting on the motor vehicle in its lateral
direction; and
inhibiting the signal representing the determined new transmission speed
ratio to the automatic transmission when the detected lateral acceleration
exceeds a predetermined reference value.
15. A change transmission speed ratio control method for an automatic
transmission in a motor vehicle according to claim 13, wherein said
selecting step is performed by retrieving a change transmission speed
ratio characteristic map having map retrieval inputs of engine torque and
engine rotational speed and having a single line determining transmission
speed ratio changing points represented by engine rotational speed for the
respective engine torque.
16. A change transmission speed ratio control method according to claim 13,
wherein said determined new transmission speed ratio is one of a
predetermined number of respective speed ratios.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a control device for a motor vehicle
provided with a transmission mechanism, and in particular, relates to a
change gear control device suitable for controlling an automatic
transmission in a motor vehicle provided with a torque converter.
Conventional change gear control devices for automatic transmissions in
motor vehicles are, for example, disclosed in JP-A-51-44763 (1976) and
JP-A-62-261745 (1987) wherein a vehicle speed and a throttle valve opening
degree are detected in a form of electrical signals and a transmission
gear ratio appropriate to the instant vehicle speed and the throttle valve
opening degree is selected among a predetermined change gear pattern by
making use of the vehicle speed and the throttle valve opening degree as
variables and further wherein a plurality of change gear patterns such as
economic type driving pattern and sporty type driving pattern are prepared
and are switched via change gear pattern selection operation by the
driver.
With the above conventional change gear control devices, an intention of a
driver was not sufficiently reflected to the change gear control device
and the transmission gear control was determined by the selected instant
transmission gear pattern allowing little modification so that a proper
transmission gear ratio correctly reflecting the instant driving condition
could not be obtained, therefore the driver had to frequently switch the
change gear patterns to meet the instant driving condition which reduced
operation facility of the motor vehicle.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a change gear control
device for an automatic transmission in a motor vehicle which requires no
additional driving operation as in the conventional ones, correctly
reflects the intention of the driver and improves the operation facility
of the motor vehicle.
For achieving the above object, the change gear control device for an
automatic transmission in a motor vehicle according to the present
invention is provided with a change gear ratio processing means which
determines a transmission gear ratio for the transmission mechanism based
upon detected value of the engine torque and a detected value of the
travelling speed of the motor vehicle or based upon a detected value of
the engine torque and a detected value of the engine rotation number of
the motor vehicle.
The change gear ratio processing means determines the transmission gear
ratio for the transmission mechanism based upon the detected engine torque
rather than the throttle valve opening degree corresponding to an
acceleration pedal depression. The parameter of the engine torque more
closely meets the intention of the driver dependent upon respective
driving conditions of the motor vehicle than that of the throttle valve
opening degree. Namely, even at a same throttle valve opening degree,
engine torque shows different rise characteristics due to differences such
as vehicle weight and road surface resistance. For this reason, for
example, when the weight of the vehicle is heavy, a shift-up timing
according to the present invention is considerably delayed under an
identical change gear pattern in comparison with that of the conventional
change gear control devices which use the throttle valve opening degree
for determining the transmission gear ratio, accordingly a change gear
ratio control for the automatic transmission which highly meets the actual
driving conditions of the motor vehicle has been achieved.
According to the present invention, a desirable change gear control for an
automatic transmission in a motor vehicle which meets the intention of the
driver is obtained without necessitating switching of the change gear
patterns in such a manner that the performance of the motor vehicle is
fully utilized depending upon driving conditions while permitting an
improved operation facility for the driver of the motor vehicle.
BRIEF EXPLANATION OF THE DRAWINGS
FIG. 1 is a block diagram showing one embodiment of the change gear control
device for an automatic transmission in a motor vehicle according to the
present invention;
FIG. 1a is an alternative embodiment using a torque sensor;
FIG. 2 is a flow chart for explaining the operation of the embodiment shown
in FIG. 1;
FIG. 2a is a flow chart of the operation of the FIG. 1a embodiment;
FIG. 3 is a change gear characteristic map used in the embodiment in FIG.
1;
FIG. 4 is a block diagram showing another embodiment of the change gear
control device for an automatic transmission in a motor vehicle according
to the present invention;
FIG. 5 is a flow chart for explaining the operation of the embodiment shown
in FIG. 4;
FIG. 6 is another change gear characteristic map used in the embodiment
shown in FIG. 4;
FIG. 7 is a flow chart showing a modification of step 58 in FIG. 5;
FIG. 8 is a flow chart for explaining a further modification which may be
added to the embodiments shown in FIG. 1 and FIG. 4.
FIG. 9 is an engine torque characteristic curve dependent upon air/fuel
ratio (A/F) change under a condition when both throttle valve opening and
engine speed are kept constant;
FIG. 10 shows output shaft torque characteristic curves and vehicle speed
curves for air/fuel ratios of 14.7 and 19 with respect to time when the
throttle valve opening is kept constant;
FIG. 11(a) is a diagram prepared by overlapping an A/F change boundary line
with a conventional change gear characteristic diagram using throttle
valve opening and vehicle speed as change gear parameters for explaining
timings of change gear;
FIG. 11(b) is a graph illustrating a relationship between output shaft
torque and vehicle speed for air/fuel ratios of 14.7 and 19 for explaining
timings of change gear when the change gear is performed based on the
conventional change gear characteristic diagram as illustrated in FIG.
11(a);
FIG. 12(a) is a change gear characteristic diagram according to the present
invention using engine torque and vehicle speed as change gear parameters
for explaining the timing change of gear change depending on the air/fuel
ratio change;
FIG. 12(b) is a graph illustrating a relationship between output shaft
torque and vehicle speed for air/fuel ratios of 14.7 and 19 for explaining
timings of change gear when the change gear is performed based on the
change gear characteristic diagram according to the present invention as
illustrated in FIG. 12(a).
DETAILED EXPLANATION OF THE EMBODIMENTS
Hereinbelow, the change gear control device for an automatic transmission
in a motor vehicle according to the present invention is explained in
detail with reference to the embodiments as shown.
FIG. 1 shows one embodiment of the present invention which comprises an
acceleration detector 1, a vehicle travelling speed detector 2, a change
gear ratio processor 3 and an automatic transmission 4 of a motor vehicle,
now shown.
The acceleration detector 1 consists of such as an acceleration sensor and
functions to detect a vehicle acceleration a in its travelling direction.
The vehicle travelling speed detector 2 consists of such as a sensor which
detects a rotating speed of the vehicle propeller shaft and functions to
detect a vehicle travelling speed V.
The change gear ratio processor 3 consists of a microcomputer, determines
the engine torque Te based upon the detected acceleration a and calculates
a transmission gear ratio with reference to a change gear characteristic
map contained therein by making use of the determined engine torque Te and
the vehicle travelling speed V as its retrieval inputs.
The automatic transmission 4 consists of a torque converter and a planetary
gear mechanism and functions to switch the transmission gear ratio in the
driving system disposed between the engine and the driven wheels by making
use of a control signal fed from the change gear ratio processor 3.
Now, the operation of the present embodiment is explained with reference to
the flow chart shown in FIG. 2. The processing shown in the flow chart is
adapted to be performed by the microcomputer in the change gear ratio
processor 3 at a predetermined time period via such as a timer
interruption and when the process starts, at first in step 20 the vehicle
travelling speed V from the vehicle travelling speed detector 2 is read,
thereafter, in step 21 the acceleration a from the acceleration detector 1
is read. Further, in step 22 the value of transmission gear ratio i now in
use is read from the automatic transmission 4.
Subsequently, in step 23 based upon the acceleration a and the value of
instant transmission gear ratio i, the engine torque Te at this moment is
calculated. Namely, calculation of Te=f(a,i) is performed. The engine
torque Te may be obtained by a predetermined torque map having retrieval
inputs of the acceleration a and the value of instant transmission gear
ratio i.
In step 24, whether or not switching of the transmission gear ratio at this
moment is necessary is determined by making use of the change gear
characteristic map shown in FIG. 3 with reference to the determined engine
torque Te, the read vehicle travelling speed V and the read value of the
instant transmission gear ratio i and when it is determined that the
switching of the transmission gear ratio is necessary, in step 25 based
upon the determination in the preceding step a new transmission gear ratio
i' is output to the automatic transmission 4 to complete the processing.
In other words, when the read value of the instant transmission gear ratio
i is at the first gear speed but the point on the change gear
characteristic map determined by the determined engine torque Te and the
read vehicle travelling speed V locates in a region of the second gear
speed, the change gear ratio processor 3 determines to switch the
transmission gear ratio from the first gear speed to the second gear speed
and output a new transmission gear ratio i corresponding to the second
gear speed to the automatic transmission 4.
In the change gear control for the conventional automatic transmission, a
predetermined transmission gear ratio was selected in a selected
predetermined change gear pattern by making use of the variables of the
vehicle travelling speed and the throttle valve opening degree as
explained above. Therefore, with the conventional change gear control, it
was difficult to correctly switch the transmission gear ratio in response
to the variation of driving conditions, in particular, the variation of
load on the vehicle during travel. For example, when travelling on a flat
road or a gentle downhill road it is considered preferable to hasten the
shift-up timing in comparison with a travel on an uphill road in order to
improve fuel consumption without sacrificing the driving performance.
However, in the conventional change gear control which was determined by
making use of the throttle valve opening degree and the vehicle travelling
speed, such change gear control could not be realized unless the change
gear patterns were switched. Such change gear patterns are similar to the
change gear characteristic map shown in FIG. 3 except that the throttle
valve opening degree was used as the ordinate variable.
However, in the present embodiment, the change gear control is carried out
dependent upon the engine torque, the switching timing of a change in the
gear ratio varies even at an identical throttle valve opening degree, and
even under an identical change gear pattern the shift-up timing is delayed
when the load on the vehicle during travel is heavy and is hastened when
the load is light, so that a correct switching of transmission gear ratio
depending upon driving conditions of the vehicle is realized to thereby
achieve an improvement in driving performance of the vehicle as well as in
fuel consumption.
In the present embodiment, the engine torque is determined by calculation
by making use of the vehicle acceleration in its travelling direction
which is detected by the acceleration detector, such that a special torque
sensor is eliminated which minimizes the manufacturing cost increase of
the present embodiment. However, in place of the acceleration detector 1 a
torque sensor may be used, in such instance the engine torque is directly
detected therewith and is inputted to the change gear ratio processor 3.
FIG. 4 shows a block diagram of another embodiment according to the present
invention wherein the same or equivalent elements as in the first
embodiment are designated by the same reference numerals. In FIG. 4 an
engine rotation number detector 5 functions to detect an engine rotation
number Ne as the name indicates which is constituted to determine the
engine rotation number Ne by counting pulses from a pulse generator such
as a crank angle sensor mounted on the engine crank shaft.
A difference of the present embodiment shown in FIG. 4 from the first
embodiment shown in FIG. 1 is that the engine rotation number detector 5
is provided in place of the vehicle travelling speed detector 2 in FIG. 1
and wherein by making use of the engine rotation number Ne itself other
than the vehicle travelling speed V and the engine torque Tea transmission
gear ratio is calculated and determined.
Now, the operation of the present embodiment shown in FIG. 4 is explained
with reference to the flow chart shown in FIG. 5.
The processing shown in the flow chart in FIG. 5 is adapted to be performed
by a microcomputer in a change gear ratio processor 3 at a predetermined
time period via such as a timer interruption. When the process starts, at
first stage in steps 50, 51 and 52 an engine rotation number Ne,
acceleration a and the instant transmission gear ratio i of the automatic
transmission 4 are sequentially read in, and further, in step 53, the
engine torque Te is calculated based upon these data. The processing in
steps 51 through 53 is the same as that in steps 21 through 23 in FIG. 2
in connection with the first embodiment.
In step 54, it is judged whether or not the engine torque Te now determined
indicates a finite value and when the result of the judgment is NO, namely
when the engine torque Te is determined zero which implies that no
switching of the transmission gear ratio is needed, the process proceeds
to step 55 wherein the instant transmission gear ratio i is output as a
new transmission gear ratio i' to maintain the instant transmission gear
ratio and to complete the processing.
On the other hand, when the result of the judgment in step 54 is YES,
namely when the engine torque Te is determined a finite value which
implies that switching of the transmission gear ratio may be needed, and
the process proceeds to steps 56 through 59 to determine a new
transmission gear ratio i'. In the present processing the engine torque Te
is calculated based upon the acceleration a detected by the acceleration
detector 1 so that even if the calculated engine torque Te is zero, the
actual engine torque is not necessarily implied to be zero.
In step 56, the present vehicle travelling speed Vsp(Km/h) is calculated
based upon the present engine rotation number Ne, the present gear ratio
i, the final reduction gear ratio of the differential gear i end, and the
outer diameter L(m) of the driving wheel in accordance with the following
equation.
Vsp=(Ne)/(ix i end)xL.times.(60)/(1000) (1)
In step 57, target engine rotation numbers N.sub.1, N.sub.2, N.sub.3 and
N.sub.4 for the respective gear ratios i.sub.1, i.sub.2, i.sub.3 and
i.sub.4 corresponding to the first, second, third and fourth gear speeds
are calculated by making use of the calculated Vsp in accordance with the
following equations.
N.sub.1 =kx i.sub.1 .times.Vsp
N.sub.2 =kx i.sub.2 .times.Vsp
N.sub.3 =kx i.sub.3 .times.Vsp
N.sub.4 =kx i.sub.4 .times.Vsp (2)
wherein k is a constant.
Subsequently, in step 58, the change gear characteristic map shown in FIG.
6 is retrieved, in that since the engine torque Te has been determined in
step 53, the target engine rotation numbers N.sub.1, N.sub.2, N.sub.3 and
N.sub.4 corresponding to the respective transmission gear ratios can be
plotted on the change gear characteristic map as shown in the block of
step 58 wherein the solid line indicates shift-up points and the target
engine rotation numbers determined by the respective gear ratios above the
solid line indicate those to be selectable as a target engine rotation
number, and the nearest target engine rotation number to the solid line,
in the present instance N.sub.2 is selected and outputted to step 59. In
step 59, based upon the inputted target engine rotation number N.sub.2 a
new transmission gear ratio i' is determined and outputted to the
automatic transmission to complete the present processing.
Now, the switching operation of the transmission gear ratio by making use
of the simple change gear characteristic map shown in FIG. 6 is explained
in detail.
When the engine torque Te is on the horizontal line passing through point
A, the switching of the transmission gear ratio is caused at the engine
rotation number Ne of about 3000 (rpm). After the switching of gear ratio
the engine rotation number Ne at once reduces to the vicinity of 2000
(rpm) and then the engine rotation number Ne again rises up to the point A
near 3000 (rpm) because the engine torque Te is maintained unchanged and
when the engine rotation number reaches the shift-up point indicated by
the solid line the automatic transmission is shifted-up again.
On the other hand, when the instant transmission gear ratio i of the
automatic transmission 4 is at the third gear speed and at point B on the
change gear characteristic map and the engine torque Te suddenly changes
up to point C, this implies that the driver wants to generate a large
driving torque through shift-down. In other words, the increase of the
engine torque Te from point B to point C is initiated by the acceleration
pedal depression by the driver. As a result, the acceleration under the
instant transmission gear ratio i is increased to thereby cause the engine
torque increase. In this instance, via the processing in steps 58 and 59 a
new transmission gear ratio i' is provided to shift-down the transmission
gear ratio. Namely, since the instant gear ratio i is at the third gear
speed position indicated by point C, when the second gear speed
corresponding to gear ratio i.sub.2 indicated by point D(2) is selected
the engine rotation number Ne rises up to slightly below 4000 (rpm) and
likely when the first gear speed corresponding to gear ratio i.sub.1
indicated by point E(1) is selected the engine rotation number Ne rises up
to above 5000 (rpm) to thereby obtain a large acceleration.
In the present embodiment too, the gear change is carried out dependent
upon the engine torque, the switching time of change in gear ratio varies
even at an identical throttle valve opening degree, and even under an
identical change gear pattern the shift-up timing is delayed when the load
on the vehicle during travel is heavy and is hastened when the load is
light so that a correct switching of the gear ratio depending upon driving
conditions of the vehicle is realized to thereby achieve an improvement in
driving performance of the vehicle as well as in fuel consumption.
FIG. 7 shows a flow chart which is a modification of the processing in step
58 shown in FIG. 5. In step 58, the change gear characteristic map shown
in FIG. 6 is used to determine a target engine rotation number Nn.
However, in the modified step 580 shown in FIG. 7, instead of using the
change gear characteristic map, in step 581 the engine rotation number Ne
at the shift-up point is calculated according to the following equation.
Ne=k.sub.1 .times.Te (3)
wherein k is a constant.
In step 582, the calculated engine rotation number Ne at the shift-up point
is compared with the respective target engine rotation numbers N.sub.1,
N.sub.2 and N.sub.3 calculated previously to obtain the respective
following differences:
.DELTA.N.sub.1 =Ne-N.sub.1
.DELTA.N.sub.2 =Ne=N.sub.2
.DELTA.N.sub.3 =Ne-N.sub.3 (4)
Via steps 583 through 589, one of the target engine rotation numbers
N.sub.1, N.sub.2, N.sub.3 and N.sub.4 is selected to determine a new
transmission gear ratio i' in step 59.
A further embodiment which may be added to the first and second embodiments
is explained with reference to the flow chart in FIG. 8.
In the first and second embodiments, as will be understood from the flow
charts shown in FIG. 2 and FIG. 5 explaining the processing in the change
gear ratio processor 3, once the change gear ratio processor 3 judges that
the transmission gear ratio is to be switched, the judgment is immediately
transmitted to the automatic transmission 4 and the gear ratio is
switched.
However, when a large lateral force is acting on the vehicle such as when
the vehicle is travelling along a sharply curved road at a comparatively
high speed, if the switching of the gear ratio is performed the driving
stability of the motor vehicle may be endangered.
For preventing such drawback, in the present embodiment, an acceleration
sensor which is capable of detecting an acceleration appearing in right
and left directions of the vehicle is added, and in step 70 the output a'
from the additional acceleration sensor is detected. In step 71 a lateral
force T is calculated according to a predetermined function F=h(a'), and
further in step 72, it is judged whether or not the absolute value of the
lateral force 1T1 exceeds a predetermined reference value s, and when the
judgment result is YES, in that, 1T1>s, the process goes to step 73
through which a signal inhibiting switching of the gear ratio is outputted
to prevent the switching of the gear ratio in the automatic transmission
4.
Accordingly, with the present embodiment, the switching of the gear ratio
is inhibited when a lateral force beyond the predetermined reference value
is acting on the vehicle which is experienced such as when the vehicle is
travelling along a sharply curved road.
The above embodiment is easily realized without much increase in the
manufacturing cost thereof, because in the first and second embodiments an
acceleration sensor which detects an acceleration in the vehicle
travelling direction is already incorporated. It is only necessary to
modify the acceleration sensor to be able to detect an acceleration in the
vehicle lateral direction in addition to that in the vehicle travelling
direction.
The present invention can be used in combination with any type of internal
combustion engine. In particular, it has been discovered that an inherent
advantage of the present invention is that it is compatible with an
internal combustion engine which is designed to operate over a wide range
of air/fuel ratios including fuel lean mixture air/fuel ratios greater
than an air/fuel ratio 14.7 of stoichiometry. Conventional automatic
transmission change gear control devices cannot operate satisfactorily
with such lean fuel mixture air/fuel ratios.
Such an internal combustion engine which is designed to be operable in a
condition of a fuel lean air/fuel mixture is hereinafter referred to as a
lean burn engine. An example of such an engine is described in an article
by David Monroe et al., "Evaluation of a Cu/Zeolite Catalyst to Remove Nox
from Lean Exhaust", SAE Technical Paper Series 930737, Mar. 1-5, 1993,
pages 195-203, which is hereby incorporated by reference.
FIG. 9 shows an engine torque characteristic, in particular, a lean burn
engine torque characteristic, depending on air fuel ratio (A/F) under a
condition when the throttle valve opening and the engine speed are kept
constant. As seen from FIG. 9, the available engine torque decreases as
the air/fuel ratio increases, that is, when the air/fuel mixture changes
to a fuel lean condition.
FIG. 10 shows, respectively, changes of output shaft torque and vehicle
speed at air/fuel ratios of 14.7 and 19 with respect to a time when a
motor vehicle is started from a vehicle speed of 0 with a substantially
constant throttle valve opening. This figure indicates that an available
output shaft torque and vehicle speed characteristic with respect to time
vary depending on air/fuel ratios, so that an acceleration feeling given
to the driver varies depending on the variation of air/fuel ratios even
when the throttle valve opening is kept unchanged.
The desired shift points in FIG. 10 indicate that when the engine is
operating under a fuel lean condition, for example, at an air/fuel ratio
of 19, it is desirable for meeting a driver's intention to effect a gear
shifting at a lower speed or earlier timing than when operating under a
condition of an air/fuel ratio of 14.7, i.e., at stoichiometry.
FIG. 11(a) and FIG. 11(b) are diagrams for explaining an inconvenience
which can arise when the lean burn engine is combined with the
conventional automatic transmission which makes use of throttle valve
opening and vehicle speed as the gear shifting parameters. These figures
assume that an A/F change boundary between 14.7 and 19 runs between
throttle valve openings .THETA.1 and .THETA.2. As seen from FIG. 11(a),
the gear shifting is caused at vehicle speed Vsp1 for the throttle valve
opening .THETA.1 and at vehicle speed Vsp2 for the throttle valve opening
.THETA.2. Since the throttle valve openings .THETA.1 and .THETA.2 are
substantially the same, the vehicle speeds Vspl and Vsp2 at which the gear
shifting is caused are also substantially the same. Assuming that the
throttle valve opening fluctuates from .THETA.2 to .THETA.1 during
operation and crosses the A/F change boundary from 14.7 to 19, the
available output shaft torque characteristic suddenly changes from that
for A/F of 14.7 to that for A/F of 19, as illustrated in FIG. 11(b).
However, the gear shifting is never caused until the vehicle speed reaches
Vspl which is substantially the same as Vsp2 since the throttle valve
openings .THETA.1 and .THETA.2 are substantially the same. As will be
understood from FIG. 10, it takes a longer time to reach the vehicle speed
Vspl according to the output shaft torque characteristic for the A/F of
19. Accordingly, with such a lean burn air/fuel ratio, a linear
acceleration feeling cannot be achieved in which the gear shifting is
effected at respective vehicle speeds depending upon variation of the
output shaft torque characteristics which the driver wants to obtain.
FIG. 12(a) and FIG. 12(b) are diagrams for explaining advantages when the
lean burn engine is combined with an automatic transmission according to
the present invention which makes use of engine torque and vehicle speed
as the gear shifting parameters instead of the conventional parameters. As
seen from FIG. 12(a), gear shifting is caused at vehicle speed Vsp3 for
the engine torque Te3 and at vehicle speed Vsp4 for the engine torque Te4.
Even if the throttle valve openings .THETA.1 and .THETA.2 are
substantially the same, the vehicle speeds Vsp3 and Vsp4 at which the gear
shifting is caused are substantially different. When assuming that an
operating condition of the lean burn engine changes from at an A/F ratio
of 14.7 to an A/F ratio of 19 due to factors such as fluctuation of the
throttle valve opening from .THETA.2 to .THETA.1, and that the available
output shaft torque characteristic changes suddenly from that for A/F of
14.7 to that for A/F of 19, as illustrated in FIG. 12(b), the gear
shifting is caused when the vehicle speed reaches Vsp3. This is
substantially lower than Vsp4 and is reached in shorter time. Accordingly,
a linear acceleration feeling can be realized in which the gear shifting
is effected at respective optimum vehicle speeds as illustrated in FIG.
12(b) depending upon variation of the output shaft torque characteristics
which the driver wants to obtain.
It is to be understood that the above-described arrangements are simply
illustrative of the application of the principles of this invention.
Numerous other arrangements may be readily devised by those skilled in the
art which embody the principles of the invention and fall within its
spirit and scope.
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